Bases for operating tables



June 3, 1958 E. G. GREVILLE BASES FOR OPERATING TABLES 4 Sheets-Sheet 1Filed July '7 1954 June 3, 1958 E. G. GREVILLE 2,837,387

BASES FOR OPERATING TABLES Filed July 7, 1954 4 Sheets-Sheet 3 June 3,1958 E. G. GREVILLE 2,837,387

BASES FOR OPERATING TABLES Filed July 7, 1954 /0 I III /4 4 Sheets-Sheet4 This invention relates to bases for supporting equipment, such asoperating tables, which is required to be mobile at times but is alsorequired to be firmly set or rendered immobile at other times, and theinvention is more particularly concerned with bases for such equipmenthaving hydraulic means for regulating the height thereof above thefloor.

A primary object of the invention is the provision of a base or carriagefor equipment, such as an operating table, which base can be readilyhydraulically converted from a condition in which it is mobile, onsupport means such as castors, to a condition in which it is relativelystabile, on support devices such as stump feet.

Another object of the invention is the provision of such hydraulicallyoperable support means and devices in association with hydraulicequipment adapted to regulate the i height of the supported equipmentabove the floor.

A further object of the invention is the provision of control means forensuring that the base, and thus the equipment carried thereon, isrendered immobile prior to the commencement of the elevational movementof the equipment and load.

Still further the invention has as an object the provision of controlmeans whereby the unit (comprising a base and equipment carried thereby)can alternatively be rendered either mobile or stabile without alteringthe height adjustment and whereby the height can be increased ordecreased without affecting the immobility of the unit.

Other objects and advantages of the invention will be more fullyunderstood from the description of the invention referring to theaccompanying drawings in which:

Figure 1 is a plan view of the base or carriage of the presentinvention;

Figure 2 is a side elevational view of the equipment 0 Figure 1, thisview including a diagrammatic illustration of portions of an operatingtable in association with the equipment, this view illustrating theequipment in mobile condition;

Figure 3 is a plan view of a portion of the equipment shown in Figure 1,on an enlarged scale as compared with Figure 1, this view illustratingthe pump, table lift ram and pressure release valve together with aportion of the pedal actuated mechanism for operating the pump andpressure release valve;

Figure 4 is a sectional elevation taken generally as indicated by theline 44 of Figure 3;

Figure 5 is a sectional elevational view of one of the stump feet of theinvention taken generally along the line 5-5 of Figure l but on anenlarged scale as compared with Figure 1;

Figure 6 is a sectional elevational view of the relief valve of theinvention taken generally along the line 6-6 of Figure 1;

Figure 7 is a sectional elevational view of the valve casing or junctionbox of the invention, this view being taken generally along the line 77of Figure 8; and

Figure 8 is a plan view of the valve casing illustrated in section inFigure 7.

A 2337,38? Patented June 3, 1958 Hitherto mechanical means have beenprovided for immobilizing a table, for example, a lever, cam or screwhas been adapted to raise the base olf its castors onto stump feet, or,alternatively, to lock the castor wheels.

According to the invention the base of an operating table, or likesupport, having castors, or the like, on which the base is mobile, andstump feet adapted to .render it immobile, is provided with hydraulicmeans for operating the stump feet, these means being preferably adaptedto ensure that the stump feet are automatically adjusted to anyunevenness of the floor.

When the base is applied to a table having hydraulic means forregulating the height of the table, such as a pump for supplyingpressure fluid to alifting and lowering ram, the same pump may be usedfor supplying pressure fluid to the rams or plungers of the stump feet,but means are provided to ensure that when the pump is first actuated,the stump feet are first operated to immobilize the table, after which,on further operation of the pump, the pressure fluid is permitted toflow through a relief valve, balanced to the approximate weight of thetable and patient, to the table ram to regulate its height.

Separate release valves are provided, one for the table lift ram and theother for the stump feet rams, so that the table base can be renderedmobile and immobile when required without interfering with the heightadjustment of the table; or the height of the table may be adjustedwithout rendering the base mobile.

Turning to the drawings, especially Figures 1 and 2, a base B for anoperating table T is provided with four castor wheels C. A hollow bosson the base adjacent to each castor encloses a hydraulic cylinder and isfitted with a ram or plunger having a lower enlarged cylindrical portionforming a stump foot SF (best shown in Figure 5) for engagement with thefloor.

The stump foot cylinders are connected by separate pipes to a junctionbox or valve casing VC (best shown in Figure 7) which is fitted withseparate ports and unions for the pipes. Each port is provided with aspring loaded ball check Valve. The union connections and valves arepreferably arranged radially fromthe central part of the junction box inwhich pressure fluid, such as oil, is pumped through an inlet in thecasing to which a supply pipe from a pump P (see Figures 3 and 4) isconnected, so that all the stump foot cylinders can be supplied withpressure fluid simultaneously.

In the casing forming the body of the junction box provision is made forthe simultaneous release of the check valves by means of a plungerhaving a pad or button FP which may be depressed by theoperators foot.This release of the check valves allows the fluid to return to the sumpS (Figures 1, 2, and 4) of the pump P via an additional port and conduitwhich are connected to it.

A table lift ram LR is provided with a cylinder in the extension havingan exhaust passage for pressure fluid from the table lift ram cylinder.The escape of fluid from this passage to the sump is controlled by thepressure release valve PRV which may be a ball check valve normally heldto its seat by a spring, but displaceable from the seat by a smallplunger when fluid is to be released. This plunger is guided in a boreinthe lower end of an upright cylinder and extends into this cylinderwhere it is provided with an enlargement or piston. The pressure releasevalve PRV provides for independent release of pressure fluid from thetable lift ram cylinder to the sump S.

A pedal PP is provided which may be arranged to gpierlate both the pumpP and the pressure release valve The delivery port from the pump P leadsto a passage in the base in which a spring loaded check valve CV (Figure4) is fitted. This passage interconnects near the opposite end with adelivery pipe through a union. This pipe delivers pressure fluid fromthe pump through a relief valve RV to the central inlet in thevalvecasing VC before referred to. The relief valve is provided with apipe connected with the table lift ram cylinder.

The pump is operated by the pedal PP which pedal is adapted to actuate arocker R one arm of which is adapted, when the pedal is depressed, tobear on the cross-head of the pump piston rod. The pedal is alsoconveniently adapted to operate the pressure release valve PRV of thetable lift ram. For this purpose the pedal is lifted so that a secondarm on the rocker R engages with and depresses the head of the plungeror operating rod of the release valve.

Safety exhaust ports SP (Figures 3 and 4) are provided near the upperend of the table lift ram cylinder to limit the maximum upward travel ofthe piston or lift of the table by permitting pressure fluid to escapetherethrough when the piston is raised a sufficient distance to uncoveror expose the ports SP to the pressure fluid beneath the piston.Deflectors D are provided to deflect the escaped fluid downwardly intothe sump.

There follows a more detailed description of the various parts of theinvention heretofore mentioned.

The pump P (see Figure 4) comprises an upright cylinder 9 having an openupper end, and a piston '10, the rod 11 of which extends through theopen end and has a cross head 12. The lower end of the cylinder 9 issecured to a. base or casing 13 having an inlet port 14 for the cylinderfrom the sump S, the port 14 being fitted with a check valve 15 and astrainer 16, having spaced apertures 16a (Figure 3) therethrough. Alsolocated in the base 13 of the pump is: a delivery port 17 from thecylinder. The base 13 may be secured to the floor of the sump by bolts13a and nuts: 13b.

A helical spring 18 surrounds the pump cylinder 9 and abuts at one endagainst the bottom surface 19 'of the cross head 12 and at the other endagainst the base 13. The function of this spring will be fully explainedherebelow.

The pump is further provided with guide rods 20, 20 threaded as at 21 atthe lower ends thereof and adapted to be inserted in tapped holes in thebase 13, and also threaded at the upper end thereof as at 22 forcooperation with double nuts 23 adapted for adjusting the maximum upwardtravel of the cross head 12 under the influence of the helical spring18. The cross head 12 is provided with apertures through which the guiderods 20, 20 pass.

The pump piston 10 is provided with a pair of resilient cups, the lowercup 24 being open downwardly and the upper cup 25 being open upwardly.Two oppositely acting cups are provided in this fashion in order thatthe pump will have a double acting capacity, i. e., on the up stroke ofthe piston 10 the cup 25 acts to suck oil in through the apertures 26against the force of the spring 27 normally closing the valve 15, and onthe down stroke of the piston 10 the cup 24' acts to force pressurefluid out through the exit passage 17.

Exit passage 17 interconnects with delivery passage 28 located in acentrally extending portion 29 of the base 13. This delivery passage 28passes below the lift ram mechanism LR and interconnects through a unionwith delivery pipe 30 (see Figure 1).

Pressure fluid passing out the delivery port 17 must go through checkvalve CV in order to reach delivery passage 28. Check valve CV comprisesa sleeve 31 having a screw threaded portion 32 cooperating with threads33 formed in delivery pasage 28. The check valve body 34 has anextension 35 of triangular cross section which extends into the bore 36of sleeve 31. A resilient washer 37 is provided for cooperation with thevalve seat 38. A spring 39 abuts against a collar 40 on the valve body34 and against a spring seat 41 threaded into the passage 28. Spring 39acts in direction to normally close check valve CV. Thus, for pressurefluid to pass out of the pump through delivery port 17 and into deliverypassage 28, the pressure of the fluid must build up sufiiciently toforce the valve body 34 off of the valve seat against the action ofspring 39.

Another arm 42 of the base member extends radially outwardly from thelift ram LR in manner similar to arm 29. This arm 42 of the baseterminates in an enlargement 43 which may be secured to the floor of thesump by bolts 43a and nuts 43b.

Screw threaded into the enlargement 43 is an upright housing 44 for thepressure release valve PRV. This housing 44 terminates in a cylinder 45in which the release piston 46 operates.

In the lower portion of the housing 44 there is a ball check valve 47urged against its seat 'by spring 48 which abuts against the lower sideof the ball and against a spring seat member 49 screwed into the bottomof the bore 50 in the housing 44 against the resilient gasket 51. Thespring seat member 49 has a passage 52 therethrough communicating withexhaust passage 53 in base arm 42, which exhaust passage 53 is open tothe cylinder of the lift ram LR through port 54.

The piston 46 has an extension 55 of reduced cross section extendingdownwardly through oversize passage 56 in housing 44 into contact withthe upper side of ball check valve 47'. Ports 57 through the wall ofhousing 44 interconnect the annular space surrounding the pistonextension 55 and the sump S.

A spring '58 located in the cylinder 45 below the piston 46 and abuttingagainst the bottom of the cylinder 45 and against a shoulder on piston46, together with a spring 59 abutting against the top surface of thecylinder 45 and the bottom surface 60 of the cross head 61 on piston 46,urge the piston 46 and the extension 55 thereof upwardly.

From the above, it can be seen that depressing the cross head 61 willcause the piston 46 and the extension 55 to travel downwardly and unseatthe ball valve 47 against the spring 48. The parts in this lowerpositionopen a passageway from the lower portion of the cylinder of thelift ram LR through the port 54, the exhaust passage 53, the passage 52,the bore 50, the annular passage 56, the ports 57, and into the sump S.

The foot pedal PP is mounted for rotation with an axle 62 which isjournalled in and protrudes through the dome-shaped casing or coverplate 63 generally surrounding and overlying the sump S and enclosingthe tableram cylinder, the pump, the pressure release valve and thepedal rocker and secured to the base B by screws 64.

The rocker R is forked at each end (see Figure 3) and rollers 66, 67 aremounted on pins between the tines of the forks. The roller 66 ispositioned just above the cross head 12 of the pump and the roller 67 ispositioned just above the cross head 61 of the pressure release valvePRV.

With this arrangement, it will be seen that movement of the pedal PPdownwardly from the position shown in Figure 2 will tend to build uppressure in the fluid beneath the piston of the pump P, driving fluidout through delivery channel 17. Upon reaching the bottom of thedownward stroke, the operator lessens the force on the pedal PPsufiiciently to permit the spring 18 to return the cross head 12 to itsupper position. During this upward stroke fluid is drawn into the pumpcylinder through the check valve 15 and the pumping cycle may berepeated.

On the other hand, movement of the pedal PP in an upwardly direction asviewed in Figure 2 will depress the cross head 61 of the pressurerelease valve PRV and thus vent the cylinder of the lift ram LR to thesump. This release of the pressure fluid in the lift ram cylinder lowersthe table T and the weight carried thereon.

ass /33w Attention will now be turned to the lift ram assembly. As abovementioned, the cylinder 68 of the lift ram is mounted on the same baseas the pump P and the pressure release valve PRV. The cylinder 68 isfitted with a ram or piston 69 having a rod 70 extending beyond theupper open end of the cylinder.

The piston has a downwardly open cup 71 held in place by cup washers 72and 73.

A coiled spring 74 below the piston abuts the bottom of the cylinder anda shoulder on the lower end of the piston 69 and acts as a buffernormally holding the piston above the level of the inlet port 75. Theupper end of' the rod 76 is secured or located by suitable means to thetable to be raised and lowered.

Attention is now called to the relief valve RV best seen in Figure 6.The pipe 30 carrying pressure fluid from the pump by way of the deliverychannel 28 interconnects with a passage 7 6 near, the bottom of therelief valve RV through a union 77. Pressure fluid may flow from thepassage 76 through the union 78 and out the pipe 79 which leads to thejunction box or valve casing VC described herebelow.

An upright portion 80 of the relief valve has a bore 81 interconnectingwith the lower passage 76. The bore 81 contains a ball check valve 82 incontact with a plunger 13. A coiled spring 84- abuts at its lower end ona collar 85 on the plunger 83, while the upper end of the spring abutsagainst a collar 86 on a second plunger 87. By this arrangement, thelower plunger 83 normally holds the ball valve to its seat.

An adjusting screw 88 passes through a nut 89 and the relief valve cap90 and bears against the top of the second plunger 87. By these meansthe pressure of the spring 84 and, therefore, the pressure at which therelief opens can be regulated.

A cover 91 protects the upper portion of the relief valve mechanism.

A passage 92 communicates with the bore 81 at a point above the normal(closed) position of the ball check valve 82 and leads through a union93 to a pipe 94 which carries pressure fluid to the cylinder of the liftram LR.

During the initial portion of the pumping by means of the pedal PPpressure fluid is supplied to the stump feet through delivery channel28, pipe 30, and pipe 79 (connected at the bottom of the relief valveRV) and valve casing VC. When the stump feet have been extended intocontact with the floor under pressure suflicient to relieve the castorsC from all load, back pressure builds up sufliciently to force the checkvalve 82 into its upward open position and permit pressure fluid to passout of passage 92 and into the pipe 94 leading to the lift ram.

The arrangement is such that when the pump has supplied sufiicientpressure fluid to operate the stump feet, a few further strokes of thepump will set up sufficient pressure to open the relief valve and supplyfluid to raise the table lift ram.

Turning now to the junction box or valve casing VC of Figures 7 and 8,it will be seen that this device is of the nature of a manifoldproviding simultaneously fluid under equalized pressure to four pipesleading to the stump feet.

The pipe 79 from the relief valve RV connects through a union 95 nearthe bottom of the valve casing to the lead-in passage 96. The pressurefluid flows through the passage 96 into the manifold chamber 97. Fourequally spaced radial passages communicate with the manifold 97.Pressure fluid may flow through these four passages and appropriatefittings 98, 99, 100 and 101 into pipes 102, 103, 104 and 105.

A ball check valve is provided in each of the four exit passages leadingfrom the manifold 97. Three of these balls 106, 107 and 103 appear inthe sectional view of Figure 7. A spring such as 109 and 110 associatedwith each ball holds the ball normally against the seat and concludesbackflow from stump feet SF.

A return passage 111 leads upwardly from the mamfold 97 and communicateswith a return pipe 112 to the sump S. The return passage 111 has formedat its lower end a valve seating. The plunger rod 113 has at its lowerend an enlargement 114 which has a conical upper surface which isnormally held by spring 115 against the seating formed at lower end ofreturn passage 111, forming a valve which occludes the passage ofpressure fluid from manifold chamber 97 to the return passage 111. Whenthe rod 113 is displaced downwardly the valve opens and the lowersurface of the enlargement 114.

simultaneously displaces the four ball check valves as 106 from theirseats and pressure fluid is allowed to pass from pipes 101, 102, 103,104 through manifold chamber 97 to return passage 111. A foot pad isattached to the upper end of rod 113 and a spring 115 urges the foot padand rod assembly towards its upward position. cover plate 116 isprovided with attachment screws 117 for ease in removing, repairing,etc., the valve casing assembly.

The pipe 102 interconnects with stump foot 118, pipe 103 with stump foot119, pipe 104 with stump foot 120, and pipe 105 with stump foot 121.Since all four of the stump feet are alike in construction andoperation, a detailed description of stump foot 119, referringparticularly to Figure 5, will be sufficient.

The stump foot pad 122 is carried on the piston 123 and fastened theretoby means of the threaded portion 124 and the nut 125. A plate or washer126, for instance of rubber, may be secured by a screw 127 to the bottomsurface of the stump foot pad 122 to provide a desirable surface forcontact with the floor. Pressure fluid from the pipe 103 may flowthrough the passage 128 into the stump foot cylinder 129 above the cup130 on the top of the piston 123.

A spring 131 surrounds the piston 123 and abuts against a shoulder 132and said piston and against a shouldered boss 134 bolted to the lowersurface of the cylinder casting 134a. Spring 139 urges the piston andthus the stump foot toward the upward or retracted position out ofcontact with the floor.

A contact of the piston body with the boss 134 and also with shoulder135 of the cylinder limits the upward travel of the stump foot andpiston. Downward travel of the stump foot and piston is limited by theshoulders 132 and 133 and the bottoming of the spring 131 locatedtherebetween.

The stump foot cylinder 129 is provided at the top thereof with ableeder valve 136, which is normally closed but may be opened whenrequired to allow any air present to escape. A protective cap 137 isfitted over the top of the stump foot cylinder and the bleeder valve.

With the foregoing detailed description in mind, a brief summary of theoperation of the invention follows.

When the equipment is in the condition shown in Figure 2, it is readilymobile on the castors C and can be moved from place-to-place at will.

Repeated downward pumping action on the foot pedal PP causes delivery ofpressure fluid from the pump P to the relief valve RV. At first thepressure fluid will flow through the relief valve and the valve casingVC, and from there to the four stump feet SF. This results in extendingthe stump feet into contact with the floor and thus results in thebearing of the load on the stump feet instead of the castors C. Thestump feet will be extended greater or lesser distances as may benecessary to compensate for any unevenness in the floor by reason of thepressure equalizing characteristics of the hydraulic system suppliedfrom a common source in the manifold of the valve casing VC.

When the stump feet are extended the pressure will build up in the fluidlines leading from the stump feet to the valve casing VC and thus in thefluid line leading to the relief valve RV. The increased pressure openscheck valves (106 and 108) effectively prevent release of pressure inthe stump foot cylinders.

When the lift ram is extended upwardly sufficiently far that the safetyports SP communicate with the cylinder below the piston cup 71, nofurther upward travel of the lift ram is possible since the pressurefiuid escapes through the safety ports SP and returns to the sump S.

If it is desired to lower the table, this can be accomplished withoutrendering the unit mobile by lifting up on the pedal PP and thus openingthe pressure release valve PRV and venting the lift ram cylinder to thesump. It is thus seen that, after the stump feet are initially extended,operating the pedal PP in one direction or the other will adjust theheight of the operating table Withoutaffecting the position of the stumpfeet.

If it is desired to wheel the table to some other location, this can beaccomplished by depressing the foot pad PP and thus venting the stumpfeet cylinders to the sump. This will result in retraction of the stumpfeet and a reassumption of the load by the castors and this will notaffect the position of the lift ram LR because of the occlusion ofbackfiow by the ball 82 in the relief valve RV. After the table has beenmoved to the desired location, pumping downwardly on the foot pedal willagain extend the stump feet without afiecting the height adjustment.

1 claim:

1. In a base for supporting equipment such as an operating table or thelike, said base being movable on a plurality of casters, the combinationof a hydraulic lift for altering the vertical position of the supportedequipment, a plurality of stump feet for said base vertically movablebetween retracted positions out of contact with the floor and extendedpositions in contact with the floor, said stump feet in the extendedpositions supporting the base independently of said casters, a junctionbox, a

plurality of fluid passage means between said junction box and each ofsaid stump feet, a plurality of simultaneously operable check valves insaid junction box, one in each of said passage means and normallyoccluding flow in direction to retract said stump feet, a hydraulic pumpcarried on said base, fluid connections from the pump to the lift andfrom the pump to the junction box, a relief valve interposed in saidlast named connections and operable upon extension of said stump feet todeliver pressure fluid to the lift, means for releasing the pressure tosaid lift, and means for disabling; said check valves independently ofthe release of pressure to said lift.

2. A mobile unit for supporting equipment such as an operating table orthe like, comprising a base member, a plurality of stiunp feet mountedtherein and adapted to immobilize said unit, a lift ram for altering thevertical position of the supported equipment, first fluid pressurepiston and cylinder means operable to condition said stump feet toimmobilize said unit and second such means operable to raise said liftram, a pump and a sump for supplying fluid thereto, pressure fluiddelivery means interconnecting said pump and said first and secondpiston and cylinder means, valve mechanism in said delivery meansadapted to permit flow to said second piston and cylinder means to raisesaid lift ram automatically upon completion of operation of said firstpiston and cylinder means to immobilize said unit, and returnconnections from said first and second means to the sump of said pump.

3. The mechanism of claim 2 wherein the pressure fluid delivery meansinterconnecting the pump and the first piston and cylinder meansincludes a common manifold for effecting hydraulic leveling of the stumpfeet in said cylinders.

4. A construction according to claim 2 in which said first meanscomprises a plurality of piston and cylinder devices, one associatedwith and adapted to extend and retract each of said stump feet, and saidconstruction further including a junction box interposed in the deliverymeans interconnecting the pump and said first means, said junction boxcomprising manifold means having an intake from the pump, a plurality ofdischarge outlets, each connected with one of the piston and cylinderdevices, and a return outlet connected with the sump of the pump, aspring loaded check valve in each discharge outlet normally occludingflow in direction to permit retraction of the stump feet, obturatingmeans normally closing said return outlet, and actuating meanspositioned to simultaneously displace said check valves and saidobturating means.

5. A construction according to claim 4 in which said obturating meanscomprises a valve device, said check valve in each discharge outletcomprises a ball protruding into the path of travel of said valve deviceand adapted to be displaced from its valve seat thereby, and in whichsaid actuating means is spring loaded to hold said valve device in aposition obturating flow through said return outlet and is adapted todisplace said valve device.

6. A mobile unit for supporting equipment such as an operating table orthe like, comprising a base, a plurality of stump feet mounted thereinand adapted to immobilize said unit, a lift ram for altering thevertical position of the supported equipment, first fluid pressurepiston and cylinder means operable to condition said stump feet toimmobilize said unit and second such means operable to raise said liftram, a pump and a sump for supplying fluid thereto, pressure fluiddelivery means interconnecting said pump and said first and secondpiston and cylinder means, valve mechanism in said delivery meansadapted to permit flow to said second piston and cylinder means to raisesaid lift ram automatically upon completion of operation of said firstpiston and cylinder means to immobilize said unit, and independentlyactuated control devices for venting said first and second piston andcylinder means to the sump of said pump.

7. A construction according to claim 6 and further including a pedalmounted on one end of an axle and operable to rotate said axle in eitherdirection from a neutral position, journal means for said axle connectedwith said base, a double ended rocker arm mounted on the other end ofsaid axle, one end of said rocker arm being adapted upon rotation ofsaid axle in a given direction to operate said pump, and the other beingadapted upon rotation in the opposite direction to operate said controldevice venting said second piston and cylinder means to the sump of thepump, and balanced spring means opposing rotation of said axle in eitherdirection and adapted upon release of force displacing said pedal toreturn same to the neutral position.

8. A mobile unit for supporting equipment such as an operating table orthe like, comprising a base member, a plurality of stump feet mountedtherein and adapted to immobilize said unit, a lift ram for altering thevertical position of the supported equipment, first fluid pressurepiston and cylinder means operable to condition said stump feet toimmobilize said unit and second such means operable to raise said liftram, a pump and a sump for supplying fluid thereto, pressure fluiddelivery means interconnecting said pump and said first and secondpiston and cylinder means, valve mechanism in said delivery meanscomprising a check valve normally biased toward a position occludingflow in the delivery means interconnecting the pump and the secondpiston and cylinder means but displaceable to permit such flow indirection to raise said lift ram when the pressure in the fiuid exerts aforce exceeding that of said bias, and independently actuated controldevices for venting said first and second piston and cylinder means tothe sump of said pump.

References Cited in the file of this patent UNITED STATES PATENTS 10Klipstein et a1 Nov. 11,1941 Shampaine Feb. 25, 1947 Clachko Aug. 29,1950 Shampaine Dec. 5, 1950 Gardiner Oct. 30, 1951 Shampaine July 29,1952 Murray Apr. 28, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No.. 2,837,387 June 3, 1958 Ernest Gordon Greville 7It is hereb$ certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 5, line '75 for "concludes" read occludes column 6, line 3'7,'for"and", first occurrence, read on Signed and sealed this 22nd day of July1958,

(SEAL) Attest:

' ROBERT C. WATSON Attesting Officer Commissioner of Patents

